Hi, I picked up an early G5 iMac 110V, blew the power supply, and got a universal power supply replacement. I never used to shut down or put them to sleep, and when I did a sleep light firmware update, it powered it down to then restart, except it never did. I don't remember the exact details, but swapping power supplies often did the trick to jump start either of the 2 iMacs (2nd one was a uni power supply original). I then left it alone after that didn't work anymore. Almost 2 years later, I try again, and it powered up! Except it doesn't like going to sleep or being shut down. Only a restart works to keep it on. I've done all the software updates. Testing point sto a wonky power supply. Is the ONLY solution to either never shut down or buy a new power supply? Here's the kicker. It comes on by itself very randomly if it's stuck in siesta mode. lol. Saves me having to open up the hood every time to give it soem attention. Comments!? ps. my Cube just died after a power outage. 6 years of faithful service.